Fix SanitizationFilter bugs
Fix SanitizationFilter bugs

Return a `SafeBuffer` instead of a `String` from the `#gfm_with_options`
method so that Rails doesn't escape our markup.

Also add `<span>` to the sanitization whitelist to avoid breaking syntax
highlighting in code blocks.

yama07/gitlabhq,daiyu/gitlab-zh,ordiychen/gitlabhq,ksoichiro/gitlabhq,szechyjs/gitlabhq,it33/gitlabhq,luzhongyang/gitlabhq,allysonbarros/gitlabhq,rebecamendez/gitlabhq,mente/gitlabhq,ordiychen/gitlabhq,szechyjs/gitlabhq,Tyrael/gitlabhq,jirutka/gitlabhq,jirutka/gitlabhq,Tyrael/gitlabhq,delkyd/gitlabhq,dwrensha/gitlabhq,eliasp/gitlabhq,MauriceMohlek/gitlabhq,julianengel/gitlabhq,manfer/gitlabhq,cncodog/gitlab,martinma4/gitlabhq,yatish27/gitlabhq,martinma4/gitlabhq,ferdinandrosario/gitlabhq,julianengel/gitlabhq,rhels/gitlabhq,dplarson/gitlabhq,MauriceMohlek/gitlabhq,NKMR6194/gitlabhq,nmav/gitlabhq,flashbuckets/gitlabhq,yuyue2013/ss,johnmyqin/gitlabhq,mrb/gitlabhq,williamherry/gitlabhq,koreamic/gitlabhq,zBMNForks/gitlabhq,since2014/gitlabhq,LUMC/gitlabhq,copystudy/gitlabhq,mente/gitlabhq,Razer6/gitlabhq,fgbreel/gitlabhq,fendoudeqingchunhh/gitlabhq,folpindo/gitlabhq,allysonbarros/gitlabhq,michaKFromParis/sparkslab,fearenales/gitlabhq,theodi/gitlabhq,rumpelsepp/gitlabhq,jvanbaarsen/gitlabhq,hzy001/gitlabhq,michaKFromParis/sparkslab,vjustov/gitlabhq,k4zzk/gitlabhq,yonglehou/gitlabhq,dreampet/gitlab,since2014/gitlabhq,tempbottle/gitlabhq,flashbuckets/gitlabhq,lvfeng1130/gitlabhq,stanhu/gitlabhq,ayufan/gitlabhq,salipro4ever/gitlabhq,yatish27/gitlabhq,louahola/gitlabhq,fgbreel/gitlabhq,chenrui2014/gitlabhq,daiyu/gitlab-zh,delkyd/gitlabhq,ferdinandrosario/gitlabhq,fscherwi/gitlabhq,hacsoc/gitlabhq,larryli/gitlabhq,cinderblock/gitlabhq,martijnvermaat/gitlabhq,fscherwi/gitlabhq,sakishum/gitlabhq,axilleas/gitlabhq,michaKFromParis/gitlabhqold,michaKFromParis/gitlabhqold,michaKFromParis/gitlabhq,koreamic/gitlabhq,since2014/gitlabhq,fendoudeqingchunhh/gitlabhq,jrjang/gitlabhq,OlegGirko/gitlab-ce,rebecamendez/gitlabhq,mente/gitlabhq,Soullivaneuh/gitlabhq,kitech/gitlabhq,mr-dxdy/gitlabhq,cinderblock/gitlabhq,SVArago/gitlabhq,Exeia/gitlabhq,openwide-java/gitlabhq,michaKFromParis/gitlabhq,jvanbaarsen/gitlabhq,Burick/gitlabhq,joalmeid/gitlabhq,openwide-java/gitlabhq,yuyue2013/ss,shinexiao/gitlabhq,Razer6/gitlabhq,pulkit21/gitlabhq,screenpages/gitlabhq,sakishum/gitlabhq,bigsurge/gitlabhq,openwide-java/gitlabhq,hq804116393/gitlabhq,zBMNForks/gitlabhq,SVArago/gitlabhq,sekcheong/gitlabhq,OtkurBiz/gitlabhq,ikappas/gitlabhq,larryli/gitlabhq,dreampet/gitlab,allistera/gitlabhq,johnmyqin/gitlabhq,yuyue2013/ss,whluwit/gitlabhq,rumpelsepp/gitlabhq,dplarson/gitlabhq,nguyen-tien-mulodo/gitlabhq,sakishum/gitlabhq,manfer/gitlabhq,joalmeid/gitlabhq,hzy001/gitlabhq,fpgentil/gitlabhq,jrjang/gitlab-ce,revaret/gitlabhq,htve/GitlabForChinese,tempbottle/gitlabhq,pjknkda/gitlabhq,fgbreel/gitlabhq,fantasywind/gitlabhq,k4zzk/gitlabhq,luzhongyang/gitlabhq,sonalkr132/gitlabhq,mente/gitlabhq,childbamboo/gitlabhq,initiummedia/gitlabhq,gorgee/gitlabhq,ksoichiro/gitlabhq,delkyd/gitlabhq,dukex/gitlabhq,Exeia/gitlabhq,sonalkr132/gitlabhq,nguyen-tien-mulodo/gitlabhq,yama07/gitlabhq,daiyu/gitlab-zh,dvrylc/gitlabhq,gopeter/gitlabhq,darkrasid/gitlabhq,tim-hoff/gitlabhq,ayufan/gitlabhq,cui-liqiang/gitlab-ce,Tyrael/gitlabhq,daiyu/gitlab-zh,Devin001/gitlabhq,larryli/gitlabhq,yfaizal/gitlabhq,nguyen-tien-mulodo/gitlabhq,bigsurge/gitlabhq,mavimo/gitlabhq,eliasp/gitlabhq,copystudy/gitlabhq,initiummedia/gitlabhq,pjknkda/gitlabhq,youprofit/gitlabhq,flashbuckets/gitlabhq,gorgee/gitlabhq,NKMR6194/gitlabhq,chadyred/gitlabhq,folpindo/gitlabhq,it33/gitlabhq,tempbottle/gitlabhq,NARKOZ/gitlabhq,ksoichiro/gitlabhq,cui-liqiang/gitlab-ce,LUMC/gitlabhq,TheWatcher/gitlabhq,zrbsprite/gitlabhq,luzhongyang/gitlabhq,michaKFromParis/sparkslab,jirutka/gitlabhq,fantasywind/gitlabhq,bozaro/gitlabhq,mmkassem/gitlabhq,childbamboo/gitlabhq,fscherwi/gitlabhq,hacsoc/gitlabhq,revaret/gitlabhq,rhels/gitlabhq,yfaizal/gitlabhq,duduribeiro/gitlabhq,dukex/gitlabhq,liyakun/gitlabhq,fearenales/gitlabhq,flashbuckets/gitlabhq,screenpages/gitlabhq,Telekom-PD/gitlabhq,icedwater/gitlabhq,zrbsprite/gitlabhq,iiet/iiet-git,dreampet/gitlab,LytayTOUCH/gitlabhq,screenpages/gitlabhq,fpgentil/gitlabhq,WSDC-NITWarangal/gitlabhq,mr-dxdy/gitlabhq,julianengel/gitlabhq,bbodenmiller/gitlabhq,iiet/iiet-git,martinma4/gitlabhq,hzy001/gitlabhq,openwide-java/gitlabhq,youprofit/gitlabhq,whluwit/gitlabhq,DanielZhangQingLong/gitlabhq,OtkurBiz/gitlabhq,per-garden/gitlabhq,initiummedia/gitlabhq,sue445/gitlabhq,manfer/gitlabhq,fearenales/gitlabhq,Tyrael/gitlabhq,DanielZhangQingLong/gitlabhq,LUMC/gitlabhq,revaret/gitlabhq,revaret/gitlabhq,theonlydoo/gitlabhq,zrbsprite/gitlabhq,jvanbaarsen/gitlabhq,DanielZhangQingLong/gitlabhq,dvrylc/gitlabhq,Devin001/gitlabhq,bbodenmiller/gitlabhq,joalmeid/gitlabhq,stanhu/gitlabhq,nmav/gitlabhq,copystudy/gitlabhq,it33/gitlabhq,jirutka/gitlabhq,yfaizal/gitlabhq,dvrylc/gitlabhq,martijnvermaat/gitlabhq,stoplightio/gitlabhq,nmav/gitlabhq,yama07/gitlabhq,mr-dxdy/gitlabhq,t-zuehlsdorff/gitlabhq,hq804116393/gitlabhq,Devin001/gitlabhq,dwrensha/gitlabhq,DanielZhangQingLong/gitlabhq,Soullivaneuh/gitlabhq,kitech/gitlabhq,Soullivaneuh/gitlabhq,darkrasid/gitlabhq,aaronsnyder/gitlabhq,hq804116393/gitlabhq,jrjang/git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/gitlabhq,pjknkda/gitlabhq,t-zuehlsdorff/gitlabhq,luzhongyang/gitlabhq,chadyred/gitlabhq,yonglehou/gitlabhq,szechyjs/gitlabhq,sue445/gitlabhq,SVArago/gitlabhq,per-garden/gitlabhq,SVArago/gitlabhq,rumpelsepp/gitlabhq